/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.bangcommunity.bbframe.common.utils.reflect;

import com.bangcommunity.bbframe.common.utils.Assert;
import com.bangcommunity.bbframe.common.utils.lang.ConcurrentReferenceHashMap;

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Helper class for resolving generic types against type variables.
 *
 * <p>
 * Mainly intended for usage within the framework, resolving method parameter types even when they
 * are declared generically.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Sam Brannen
 * @author Phillip Webb
 * @since 2.5.2
 */
public abstract class GenericTypeResolver {

    /** Cache from Class to TypeVariable Map */
    @SuppressWarnings("rawtypes")
    private static final Map<Class<?>, Map<TypeVariable, Type>> typeVariableCache = new ConcurrentReferenceHashMap<Class<?>, Map<TypeVariable, Type>>();

    /**
     * Determine the target type for the given parameter specification.
     * 
     * @param methodParam
     *            the method parameter specification
     * @return the corresponding generic parameter type
     * @deprecated as of Spring 4.0, use {@link MethodParameter#getGenericParameterType()}
     */
    @Deprecated
    public static Type getTargetType(MethodParameter methodParam) {
        Assert.notNull(methodParam, "MethodParameter must not be null");
        return methodParam.getGenericParameterType();
    }

    /**
     * Determine the target type for the given generic parameter type.
     * 
     * @param methodParam
     *            the method parameter specification
     * @param clazz
     *            the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     */
    public static Class<?> resolveParameterType(MethodParameter methodParam, Class<?> clazz) {
        Assert.notNull(methodParam, "MethodParameter must not be null");
        Assert.notNull(clazz, "Class must not be null");
        methodParam.setContainingClass(clazz);
        methodParam.setParameterType(ResolvableType.forMethodParameter(methodParam).resolve());
        return methodParam.getParameterType();
    }

    /**
     * Determine the target type for the generic return type of the given method, where formal type
     * variables are declared on the given class.
     * 
     * @param method
     *            the method to introspect
     * @param clazz
     *            the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     * @see #resolveReturnTypeForGenericMethod
     */
    public static Class<?> resolveReturnType(Method method, Class<?> clazz) {
        Assert.notNull(method, "Method must not be null");
        Assert.notNull(clazz, "Class must not be null");
        return ResolvableType.forMethodReturnType(method, clazz).resolve(method.getReturnType());
    }

    /**
     * Determine the target type for the generic return type of the given <em>generic method</em>,
     * where formal type variables are declared on the given method itself.
     * <p>
     * For example, given a factory method with the following signature, if
     * {@code resolveReturnTypeForGenericMethod()} is invoked with the reflected method for
     * {@code creatProxy()} and an {@code Object[]} array containing {@code MyService.class},
     * {@code resolveReturnTypeForGenericMethod()} will infer that the target return type is
     * {@code MyService}.
     * 
     * <pre class="code">
     * {@code public static <T> T createProxy(Class<T> clazz)}
     * </pre>
     * 
     * <h4>Possible Return Values</h4>
     * <ul>
     * <li>the target return type, if it can be inferred</li>
     * <li>the {@linkplain Method#getReturnType() standard return type}, if the given {@code method}
     * does not declare any {@linkplain Method#getTypeParameters() formal type variables}</li>
     * <li>the {@linkplain Method#getReturnType() standard return type}, if the target return type
     * cannot be inferred (e.g., due to type erasure)</li>
     * <li>{@code null}, if the length of the given arguments array is shorter than the length of
     * the {@linkplain Method#getGenericParameterTypes() formal argument list} for the given
     * method</li>
     * </ul>
     * 
     * @param method
     *            the method to introspect, never {@code null}
     * @param args
     *            the arguments that will be supplied to the method when it is invoked (never
     *            {@code null})
     * @param classLoader
     *            the ClassLoader to resolve class names against, if necessary (may be {@code null})
     * @return the resolved target return type, the standard return type, or {@code null}
     * @since 3.2.5
     * @see #resolveReturnType
     */
    public static Class<?> resolveReturnTypeForGenericMethod(Method method, Object[] args, ClassLoader classLoader) {
        Assert.notNull(method, "Method must not be null");
        Assert.notNull(args, "Argument array must not be null");

        TypeVariable<Method>[] declaredTypeVariables = method.getTypeParameters();
        Type genericReturnType = method.getGenericReturnType();
        Type[] methodArgumentTypes = method.getGenericParameterTypes();

        // No declared type variables to inspect, so just return the standard return type.
        if (declaredTypeVariables.length == 0) {
            return method.getReturnType();
        }

        // The supplied argument list is too short for the method's signature, so
        // return null, since such a method invocation would fail.
        if (args.length < methodArgumentTypes.length) {
            return null;
        }

        // Ensure that the type variable (e.g., T) is declared directly on the method
        // itself (e.g., via <T>), not on the enclosing class or interface.
        boolean locallyDeclaredTypeVariableMatchesReturnType = false;
        for (TypeVariable<Method> currentTypeVariable : declaredTypeVariables) {
            if (currentTypeVariable.equals(genericReturnType)) {
                locallyDeclaredTypeVariableMatchesReturnType = true;
                break;
            }
        }

        if (locallyDeclaredTypeVariableMatchesReturnType) {
            for (int i = 0; i < methodArgumentTypes.length; i++) {
                Type currentMethodArgumentType = methodArgumentTypes[i];
                if (currentMethodArgumentType.equals(genericReturnType)) {
                    return args[i].getClass();
                }
                if (currentMethodArgumentType instanceof ParameterizedType) {
                    ParameterizedType parameterizedType = (ParameterizedType) currentMethodArgumentType;
                    Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
                    for (Type typeArg : actualTypeArguments) {
                        if (typeArg.equals(genericReturnType)) {
                            Object arg = args[i];
                            if (arg instanceof Class) {
                                return (Class<?>) arg;
                            } else if (arg instanceof String && classLoader != null) {
                                try {
                                    return classLoader.loadClass((String) arg);
                                } catch (ClassNotFoundException ex) {
                                    throw new IllegalStateException(
                                            "Could not resolve specific class name argument [" + arg + "]", ex);
                                }
                            } else {
                                // Consider adding logic to determine the class of the typeArg, if
                                // possible.
                                // For now, just fall back...
                                return method.getReturnType();
                            }
                        }
                    }
                }
            }
        }

        // Fall back...
        return method.getReturnType();
    }

    /**
     * Resolve the single type argument of the given generic interface against the given target
     * method which is assumed to return the given interface or an implementation of it.
     * 
     * @param method
     *            the target method to check the return type of
     * @param genericIfc
     *            the generic interface or superclass to resolve the type argument from
     * @return the resolved parameter type of the method return type, or {@code null} if not
     *         resolvable or if the single argument is of type {@link WildcardType}.
     */
    public static Class<?> resolveReturnTypeArgument(Method method, Class<?> genericIfc) {
        Assert.notNull(method, "method must not be null");
        ResolvableType resolvableType = ResolvableType.forMethodReturnType(method).as(genericIfc);
        if (!resolvableType.hasGenerics() || resolvableType.getType() instanceof WildcardType) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    /**
     * Resolve the single type argument of the given generic interface against the given target
     * class which is assumed to implement the generic interface and possibly declare a concrete
     * type for its type variable.
     * 
     * @param clazz
     *            the target class to check against
     * @param genericIfc
     *            the generic interface or superclass to resolve the type argument from
     * @return the resolved type of the argument, or {@code null} if not resolvable
     */
    public static Class<?> resolveTypeArgument(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType resolvableType = ResolvableType.forClass(clazz).as(genericIfc);
        if (!resolvableType.hasGenerics()) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    private static Class<?> getSingleGeneric(ResolvableType resolvableType) {
        if (resolvableType.getGenerics().length > 1) {
            throw new IllegalArgumentException("Expected 1 type argument on generic interface [" + resolvableType
                    + "] but found " + resolvableType.getGenerics().length);
        }
        return resolvableType.getGeneric().resolve();
    }

    /**
     * Resolve the type arguments of the given generic interface against the given target class
     * which is assumed to implement the generic interface and possibly declare concrete types for
     * its type variables.
     * 
     * @param clazz
     *            the target class to check against
     * @param genericIfc
     *            the generic interface or superclass to resolve the type argument from
     * @return the resolved type of each argument, with the array size matching the number of actual
     *         type arguments, or {@code null} if not resolvable
     */
    public static Class<?>[] resolveTypeArguments(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType type = ResolvableType.forClass(clazz).as(genericIfc);
        if (!type.hasGenerics() || type.isEntirelyUnresolvable()) {
            return null;
        }
        return type.resolveGenerics(Object.class);
    }

    /**
     * Resolve the specified generic type against the given TypeVariable map.
     * 
     * @param genericType
     *            the generic type to resolve
     * @param map
     *            the TypeVariable Map to resolved against
     * @return the type if it resolves to a Class, or {@code Object.class} otherwise
     * @deprecated as of Spring 4.0 in favor of {@link ResolvableType}
     */
    @Deprecated
    @SuppressWarnings("rawtypes")
    public static Class<?> resolveType(Type genericType, Map<TypeVariable, Type> map) {
        return ResolvableType.forType(genericType, new TypeVariableMapVariableResolver(map)).resolve(Object.class);
    }

    /**
     * Build a mapping of {@link TypeVariable#getName TypeVariable names} to {@link Class concrete
     * classes} for the specified {@link Class}. Searches all super types, enclosing types and
     * interfaces.
     * 
     * @deprecated as of Spring 4.0 in favor of {@link ResolvableType}
     */
    @Deprecated
    @SuppressWarnings("rawtypes")
    public static Map<TypeVariable, Type> getTypeVariableMap(Class<?> clazz) {
        Map<TypeVariable, Type> typeVariableMap = typeVariableCache.get(clazz);
        if (typeVariableMap == null) {
            typeVariableMap = new HashMap<TypeVariable, Type>();
            buildTypeVariableMap(ResolvableType.forClass(clazz), typeVariableMap);
            typeVariableCache.put(clazz, Collections.unmodifiableMap(typeVariableMap));
        }
        return typeVariableMap;
    }

    @SuppressWarnings("rawtypes")
    private static void buildTypeVariableMap(ResolvableType type, Map<TypeVariable, Type> typeVariableMap) {
        if (type != ResolvableType.NONE) {
            if (type.getType() instanceof ParameterizedType) {
                TypeVariable<?>[] variables = type.resolve().getTypeParameters();
                for (int i = 0; i < variables.length; i++) {
                    ResolvableType generic = type.getGeneric(i);
                    while (generic.getType() instanceof TypeVariable<?>) {
                        generic = generic.resolveType();
                    }
                    if (generic != ResolvableType.NONE) {
                        typeVariableMap.put(variables[i], generic.getType());
                    }
                }
            }
            buildTypeVariableMap(type.getSuperType(), typeVariableMap);
            for (ResolvableType interfaceType : type.getInterfaces()) {
                buildTypeVariableMap(interfaceType, typeVariableMap);
            }
            if (type.resolve().isMemberClass()) {
                buildTypeVariableMap(ResolvableType.forClass(type.resolve().getEnclosingClass()), typeVariableMap);
            }
        }
    }

    @SuppressWarnings({ "serial", "rawtypes" })
    private static class TypeVariableMapVariableResolver implements ResolvableType.VariableResolver {

        private final Map<TypeVariable, Type> typeVariableMap;

        public TypeVariableMapVariableResolver(Map<TypeVariable, Type> typeVariableMap) {
            this.typeVariableMap = typeVariableMap;
        }

        @Override
        public ResolvableType resolveVariable(TypeVariable<?> variable) {
            Type type = this.typeVariableMap.get(variable);
            return (type != null ? ResolvableType.forType(type) : null);
        }

        @Override
        public Object getSource() {
            return this.typeVariableMap;
        }
    }

}
